While there has been considerable study and development of alternative battery materials, the lead-acid battery is still the most common choice for many operations requiring rechargeable battery power, particularly when high current capacities are sought. A conventional lead-acid battery is commonly a multi-cell structure where each cell includes a set of interdigitated monopolar positive and negative plates formed of lead or lead-alloy grids containing one or more layers of electrochemically active pastes or active materials. Positive and negative plates will generally share a common separator between them to help prevent short circuits.
The paste on the positive electrode plate will generally include a material that provides lead dioxide (PbO2), when charged, which can serve as the positive active material. The negative plate contains a negative active material such as sponge lead. An acid electrolyte such as sulfuric acid is interposed between the positive and negative plates.
Traditional lead-acid batteries use heavy metal lead in constructing the plates. Consequently, as power requirements increase (thus increasing the number of plates required), the batteries become extremely heavy making them ineffective for use in applications where weight reduction is vital, such as the aircraft, electric car and vehicle fields. In an effort to resolve the weight issues related to the use of heavy lead plates, thinner plates have been developed from lighter weight materials used in place of and in combination with lead. The use of thinner, lightweight plates creates the opportunity to increase the number of plates thereby improving the power density of a lead-acid battery. However, the extent to which conventional battery performance can be improved upon is limited, as their power and energy densities are restricted by their construction.
To overcome these construction limitations of conventional lead-acid batteries, bipolar batteries have been developed that offer the potential for improvement over monopolar battery technology. Unlike conventional lead-acid battery construction, bipolar battery construction comprises a collection of electrode plates that each contain a negative active material on one side and a positive active material on the other side, hence the terms “bipolar” and “biplate”. The biplates generally are serially arranged in such a fashion that the positive side of one plate is directed toward the negative side of an opposing plate. The bipolar battery is made up of separate electrolytic cells that are defined by biplates of opposing polarities. The biplates are electrically conductive to provide a serial connection between cells.
The biplates are typically regarded as capable of providing for improved current flow over that of conventional monopolar batteries. The enhanced current flow is believed to be the result of through-plate current transfer from one polarity of the biplate to the other. That is, in a conventional monopolar battery, the current must travel from one electrode plate to another of opposite polarity via a conductive path, which commonly is circuitous and of relatively considerable length. The significantly shortened intercell current path of a bipolar battery can thereby reduce the internal resistance of the battery, making it more efficient than the conventional monopolar battery in both discharging and charging modes of operation. Accordingly, ability to reduce internal resistance permits for the construction of a bipolar battery that is both smaller and lighter than its equivalent monopolar battery, making it a highly desirable alternative for use in the aircraft, military and electric vehicle industry where considerations of size, weight or both are of major importance.
The bipolar battery, however, is not without its own difficulties and problems. A first such difficulty involves thermal temperature control within the battery and the related desire to be able to control the temperature within the battery to produce optimum battery operating efficiency. Another related issue involves the desire to discontinue the flow of electricity, effectively shutting down the battery, when the battery is operating at undesirable temperature conditions, thereby helping to avoid a potentially hazardous condition.
Also, previous bipolar battery constructions have consistently used bulky end plates secured by cumbersome external structures to ensure no edge seal ruptures. Such bipolar batteries are generally not scalable as the thickness of the end-plate must increase with larger bipolar plate size to keep end-seal ruptures and subsequent leaking from occurring. As a result, bipolar batteries have generally been practically limited to small capacities to maintain high energy densities.
Other considerations commonly relating to bipolar battery design include the ongoing desire to improve battery efficiency by one or more modifications for increasing energy production, reducing weight, reducing overall construction size, improving construction design to support internal compressive loads, reducing construction materials, or reducing assembly operations.
U.S. Pat. No. 4,275,130 discloses a bipolar lead acid battery construction that includes a biplate of conductive thermoplastic material, a separator plate adapted to carry active material, and means for containing and maintaining the active material and conductive biplate in operable assembly and electrical contact. The teachings do not appear to discuss any battery assemblies that address temperature considerations.
U.S. Pat. No. 4,510,219 discloses a lead-acid battery plate construction for use in monopolar or bipolar batteries. The plates described therein include a glass fiber sheet having a particulate tin oxide coating. The teachings of that patent do not appear directed at addressing battery temperature considerations.
U.S. Pat. No. 4,658,499 discloses a bipolar battery plate that includes metal pellets embedded in a perforated thermoplastic sheet. The disclosed thermoplastic materials are described as having a melting point below the melting point of lead, as the preferred metal pellet material. However, the teachings of that patent do not appear directed at addressing battery temperature considerations
U.S. Pat. No. 5,585,209 describes a bipolar battery plate including a titanium core surface as a means to prevent corrosion. While the preferred materials are described as promoting temperature stability within the battery, the teachings of that patent do not appear directed at addressing an automatically controlled shut-off in the event that temperatures within the battery exceed a predetermined threshold.
U.S. Pat. No. 5,593,797 describes a bipolar battery electrode having an improved electrolyte-tight seal. While disclosing the use of conductive materials in the form of fibers or pellets within the electrode core member, the teachings of that patent likewise do not appear directed at addressing an automatically controlled shut-off in the event that temperatures within the battery exceed a predetermined threshold.
U.S. Patent Publication No. 2004/0072074 discloses a bipolar battery electrode that is described as being substantially pore-free. The electrode is further described as including an uncured epoxy in combination with a titanium powder. Among other shortcomings in the teachings, the teachings of that patent likewise do not appear directed temperature control features.
Accordingly, notwithstanding the efforts in the art, until the present teachings, there has been an ongoing and continued need for a battery, more particularly a lead-acid battery, and still more particularly bipolar lead acid battery that is constructed in a manner that provides improvements over conventional bipolar battery technology in one or more of the following areas: temperature control; high-temperature shut down; increased energy production; reduced weight, reduced overall construction size, improved construction design to support internal compressive loads; reduced construction materials or reduced assembly operations.